1. Field of the Invention
This disclosure relates to an image formation apparatus and a method of controlling the image formation apparatus, and is applicable to an MFP (Multi Function Printer) including an electrophotographic color printer unit and a scanner unit, for example.
2. Description of Related Art
In image formation apparatuses to perform electrophotographic color image formation in a color printer, a color copying machine, a color MFP and the like, multiple independent image formation units are detachably provided, one after another, along a conveyance belt to convey a recording medium. Each of the image formation units mounted in the conventional image formation apparatus includes a photosensitive drum. Toner images of respective colors are formed on the photosensitive drums and are sequentially transferred in a superimposed manner onto the medium to form a color image.
In the conventional image formation apparatus as described above, a dimensional error, misalignment of mounting positions or the like of the image formation units causes misregistration in print position (superimposed position) among the toner images of the respective colors in the formed color image (hereinafter referred to as a “color misregistration”, “print misregistration” or “image formation misregistration”). This leads to a problem of deterioration in image quality. To solve this problem, the conventional image formation apparatus as described above includes a color misregistration correction processing unit to correct a misregistration in print position between the colors.
In the image formation apparatus, the color misregistration as described above may occur after the apparatus receives shocks by opening and closing of a cover due to jamming of a medium (e.g., paper conveyance failure or the like). The conventional image formation apparatus capable of color misregistration correction processing, for example, detects opening and closing operations of the cover and executes color misregistration correction in response to the closing of the cover.
As a color misregistration correction method for the conventional image formation apparatus, there has been known a method in which color misregistration detection patterns formed on photosensitive drums are transferred onto a medium conveyance belt, and a print start position of each color is corrected according to a color misregistration amount detected by a unit configured to detect the color misregistration amount among colors in the detection pattern transferred onto the belt. This print start position correction is executed every time the power is turned on, the cover is opened or closed, or a given number of sheets are printed (see, for example, Patent Document 1: Japanese Patent Application Publication No. 2001-134041).